Issues with Google photos

1) Google photos is terrible. I get a lot of gray boxes instead of thumbnails. It seems it be caching only the most recent 50 or so images. If I scroll back to two or three years ago then It will take minutes (if ever). I have a a large sd card that photos are stored on and it is nowhere near full. I also see a notice that 25 or so photos are awaiting syncing. This number grows, never drops and never goes away, even when connected to WiFi. I have cleared the cache in apps.

Any ideas?

2) How to change backup account? If I go to settings and click on the account nothing happens.